The cooling system of an automotive vehicle involves the circulation of a liquid coolant through the engine block of an internal combustion engine and then through a heat exchanger or radiator by a pump operated by the engine. The coolant removes heat from the engine block during operation, and the radiator cools the heated coolant by a forced air flow through the radiator and around a plurality of tubes therein carrying the coolant. In view of the temperature extremes in many parts of the country, the conventional coolant is an approximately 50--50 mixture of ethylene glycol with water.
Presently, automotive radiators are formed of copper and/or brass, and the ethylene glycol, with a small percentage of diethylene glycol, is diluted with water to make a 50% or lower concentration of glycol depending on the desired freezing point protection. Most manufacturers or distributors of ethylene glycol also add corrosion inhibitors to the solution; which inhibitors are usually a mixture of one or more inorganic salts, such as phosphates, borates, nitrates, nitrites, silicates and arsenates, and an organic compound, such as benzotriazole, tolyltriazole, or mercaptobenzothiazole, to prevent copper corrosion. The solution is generally buffered to a pH of 8-10 to reduce iron corrosion and to neutralize any glycolic acid formed in the oxidation of ethylene glycol.
Most manufacturers of ethylene glycol recommend a maximum of one or two years' service for their antifreeze, however, the average car owner does not follow the owner's manual instructions to maintain -20.degree. F. protection or check the coolant to see if it is rusty or dirty. Many owners only add water when the antifreeze is lost through leakage or hose breakage. In normal passenger car service, 25% of the cars require coolant system servicing after one year; and after two years, this rises to 50%. With a conventional copper-brass radiator, it is extremely important that the antifreeze mixture contains 50-55% of the correctly inhibited ethylene glycol. A reduction to 33% ethylene glycol-67% water will increase metal corrosion significantly. This is especially important with higher temperature coolant systems which are becoming more common with the increased use of emission controls.
At the present time, a concerted effort is being made by the automobile manufacturers to increase gas mileage to federally legislated standards by size and weight reduction of the automobiles. To provide weight reduction, lightweight metals and plastics are being substituted for present day heavier metal components. One such area is in the use of aluminum in place of copper and brass for automotive radiator. Aluminum provides a high heat transfer capability, however, there have been problems in dimensional stability, corrosion resistance, and in the manufacture of the aluminum structure.
In particular, the corrosion problems discussed previously are considerably accentuated for aluminum radiators and, where corrosive water is used to replace the proper ethylene glycol-water mixture due to leakage or hose breakage during operation of the vehicle, corrosion of the aluminum radiator is considerably more rapid and destructive. Thus, the present invention provides for automatic replacement of the corrosion inhibitor to avoid the corrosion problems.